As above, your best bet is probably impulse 101. There really isn't much you can do to upgrade it though but then again there isn't much need. I've got a nine ball purple bucking in mine but it's not made any noticeable difference, I just had it laying about. You could also buy an aftermarket inner barrel but it'd be a waste of money imo. You could get a metal outer barrel if you wanted the threads for a tracer or suppressor. I will say though, don't use green gas in this one during the warmer months, 144a or nuprol 1 is fine in warmer weather. I use green in mine only when it's very cold. I've not damaged mine with green gas but it's so snappy it actually puts the wind up me and it's really not needed